Fine metal particles, method for preparing said particles, coating liquid containing said fine particles for forming transparent electroconductive film, substrate with transparent electroconductive film, and display

ABSTRACT

Subjects for the invention are to provide fine metal particles which have surface resistance as low as about 10 2  to 10 4  Ω/▭, are excellent in antistatic properties, anti-reflection properties, and electromagnetic shielding properties, and are suitable for use in forming a transparent conductive coating film excellent in reliability and durability, and to provide a process for producing the fine metal particles.  
     The invention provides fine metal particles comprising iron and noniron metal, which have an average particle diameter in the range of from 1 to 200 nm and an iron content in the range of from 0.1 to 3.0% by weight. The noniron metal preferably is one or more metals selected from the group consisting of Au, Ag, Pd, Pt, Rh, Ru, Cu, Ni, Co, Sn, Ti, In, Al, Ta, and Sb. In the fine metal particles according to the invention, part of the surface of the fine metal particles may be in the form of an oxide and/or a hydroxide.

TECHNICAL FIELD

[0001] The present invention relates to fine metal particles which haveexcellent electrical conductivity because iron is contained therein in aspecific amount and which have excellent dispersion stability and areless apt to suffer ionization, particle growth, or the like inconductive coating films, and to a coating liquid for formingtransparent conductive coating films which contains the fine metalparticles and has a long pot life. The invention further relates to asubstrate with transparent conductive coating film which is obtainedwith the coating liquid for forming transparent conductive coating filmsand is excellent in antistatic properties, electromagnetic shieldingproperties, reliability, and durability. The invention furthermorerelates to a display device having a front panel comprising thesubstrate with transparent conductive coating film.

BACKGROUND ART

[0002] A transparent coating film having the functions of preventingstatic buildup and preventing reflection has hitherto been formed on asurface of the transparent substrate of a display panel for cathode raytubes, fluorescent character display tubes, or liquid-crystal displaysfor the purposes of preventing static buildup and reflection on thesurface.

[0003] Incidentally, influences of electromagnetic waves emitted fromcathode ray tubes and the like on the human body have recently become aproblem. Besides the prevention of static buildup and reflection forwhich measures have been taken, it is desired to shield from thoseelectromagnetic waves and to diminish the electromagnetic field producedby the emission of electromagnetic waves.

[0004] One method for shielding from those electromagnetic waves or thelike is to form a conductive coating film for electromagnetic waveshielding on a surface of the display panel of a cathode ray tube or thelike. However, the conductive coating film for electromagnetic shieldinghas been required to have a surface resistance as low as 10² to 10⁴ Ω/▭,in contrast to the existing antistatic conductive coating films forwhich a surface resistance of about 10⁷ Ω/▭ or lower suffices.

[0005] When a coating liquid containing a conductive oxide heretofore inuse, such as Sb-doped tin oxide or Sn-doped indium oxide, is used forforming a conductive coating film having such a low surface resistance,it is necessary that the film is formed in a larger thickness than inthe case of existing antistatic coating films. However, since aconductive coating film produces an anti-reflection effect only when ithas a thickness of about from 10 to 200 nm, use of an existingconductive oxide such as Sb-doped tin oxide or Sn-doped indium oxideresults in a coating film having heightened surface resistance. Therehas hence been a problem that it is difficult to obtain a conductivecoating film having not only excellent electromagnetic wave shieldingproperties but excellent anti-reflection properties.

[0006] Another method for forming a conductive coating film having lowsurface resistance is to use a conductive film-forming coating liquidcontaining fine particles of a metal such as Ag to form on a surface ofa substrate a coating film containing the fine metal particles. In thismethod, a dispersion of colloidal fine metal particles in a polarsolvent is used as the film-forming coating liquid containing fine metalparticles. In such coating liquids, the surface of the fine metalparticles has been treated with an organic stabilizer such as poly(vinylalcohol), polyvinylpyrrolidone, or gelatin in order to improve thedispersibility and stability of the colloidal fine metal particles.However, the conductive coating film formed from such a film-formingcoating liquid containing fine metal particles has a drawback that sincethe fine metal particles in the coating film are in contact with oneanother through the organic stabilizer, the interparticulate resistanceis high and, hence, the surface resistance of the coating film cannot below. It is therefore necessary to conduct burning at a temperature ashigh as about 400° C. after the film formation to decompose and removethe stabilizer. However, the burning at high temperatures fordecomposition and removal of the stabilizer encounters a problem thatfusion and aggregation of fine metal particles occur to thereby reducethe transparency of the conductive coating film and heighten the hazethereof. Furthermore, in the case of cathode ray tubes and the like,there also has been a problem that exposure to high temperatures causedeterioration.

[0007] The existing transparent conductive coating film containing fineparticles of a metal such as Ag has further had a problem that metaloxidation and particle growth due to ionization may occur and, in somecases, corrosion occurs, whereby the coating film is reduced inconductivity or light transmittance to impair the reliability of thedisplay device.

[0008] The applicant proposed in, e.g., JP-A-10-188681 a coating liquidfor forming transparent conductive coating films which contains finecomposite metal particles comprising two or more metals and having anaverage particle diameter of from 1 to 200 nm. However, with such finecomposite metal particles, it has been difficult to obtain a coatingliquid having a sufficiently long pot life.

[0009] The present inventors made further investigations on fine metalparticles. As a result, they have found that when a specific amount ofFe is incorporated into fine metal particles, the coating liquid forforming transparent conductive coating films has enhanced stability andgives a transparent conductive coating film having excellent durability.The invention has been thus completed.

[0010] In JP-A-11-80619,there is a description to the effect that when aslight amount of Fe is contained as an impurity, then the transparentconductive coating film formed has a more even distribution ofconductivity in the surface and has lower resistance. JP-A-11-80619further contains a description to the effect that the content of Fe inthe fine metal particles is in the range of from 0.0020 to 0.015% byweight. There also is a description to the effect that film-formingproperties become poor as the content of Fe increases. However, the finemetal particles described in JP-A-11-80619 have had a problem that thecoating liquid has insufficient stability and gives a film havinginsufficient strength and poor durability.

[0011] An object of the invention is to overcome the problems of therelated art described above and to provide fine metal particles whichhave a surface resistance as low as about 10² to 10⁴ Ω/▭, are excellentin antistatic properties, anti-reflection properties, andelectromagnetic shielding properties, and are suitable for use informing a transparent conductive coating film excellent in reliabilityand durability. Another object is to provide a process for producing thefine metal particles, a coating liquid for forming transparentconductive coating films which contains the fine metal particles, asubstrate with transparent conductive coating film, and a display devicehaving the coated substrate.

Disclosure of the Invention

[0012] The fine metal particles according to the invention are finemetal particles comprising iron and noniron metal, and are characterizedby having an average particle diameter in the range of from 1 to 200 nmand an iron content in the range of from 0.1 to 3.0% by weight.

[0013] The noniron metal preferably is one or more metals selected fromthe group consisting of Au, Ag, Pd, Pt, Rh, Ru, Cu, Ni, Co, Sn, Ti, In,Al, Ta, and Sb.

[0014] Part of the surface of the fine metal particles preferably is inthe form of an oxide and/or a hydroxide. An aqueous dispersion in whichthe concentration of the fine metal particles is 0.5% by weightpreferably has a flow electrical current potential in the range of from50 to 300 μeq/g.

[0015] The process for producing fine metal particles according to theinvention is characterized by reducing a salt of iron and a salt of oneor more noniron metals in a solvent comprising water and/or an organicsolvent in the presence of a reducing agent in such a manner as toresult in fine metal particles having an iron content in the range offrom 0.1 to 3.0% by weight.

[0016] In this process, after fine metal particles are produced byreducing the iron salt and the salt of one or more noniron metals, anoxidizing agent may be further added to oxidize at least part of thesurface of the fine metal particles.

[0017] The coating liquid for forming a transparent conductive coatingfilm according to the invention is characterized by comprising the finemetal particles and a polar solvent.

[0018] The substrate with transparent conductive coating film accordingto the invention comprises a substrate, a transparent conductivefine-particle layer disposed on the substrate, and a transparent coatingfilm formed on the transparent conductive fine-particle layer and havinga lower refractive index than the transparent conductive fine-particlelayer, and is characterized in that the transparent conductivefine-particle layer comprises the fine metal particles described above.

[0019] The display device according to the invention is characterized byhaving a front panel comprising the substrate with transparentconductive coating film as described above, the transparent conductivecoating film being formed on the outer surface of the front panel.

Best Mode for Carrying Out the Invention

[0020] The invention will be explained below in detail.

[0021] [Fine Metal Particles]

[0022] First, the fine metal particles according to the invention willbe explained.

[0023] The fine metal particles according to the invention comprise ironand noniron metal. The iron and the noniron metal, which constitute thefine metal particles, may be in the form of an alloy in a state of solidsolution or in the form of a eutectic, which is not in a state of solidsolution. Alternatively, the metals may be in such a state that an alloyand a eutectic coexist. Preferred of fine metal particles of these kindsare fine metal particles made of an alloy in a solid-solution state.This is because such fine metal particles give a conductive coating filmin which the fine metal particles are inhibited from suffering theparticle growth caused by oxidation or ionization and which sufferslittle decrease in conductivity or light transmittance and gives asubstrate with transparent conductive coating film which has highreliability.

[0024] The term “reliability” as used herein especially meansreliability in production, namely, it means that products havingsufficient performances (conductivity, transmittance, etc.) can beproduced in high yield. Especially in the invention, this reliability isattained with a coating liquid having a long pot life (havingsatisfactory coating liquid stability). Usually, the case in whichproducts having sufficient performances (conductivity, transmittance,etc.) are obtained in high yield is also regarded as high in(production) reliability regardless of the coating liquid.

[0025] Examples of the noniron metal in such fine metal particlesinclude at least one metal selected from metals such as Au, Ag, Pd, Pt,Rh, Ru, Cu, Ni, Co, Sn, Ti, In, Al, Ta, and Sb.

[0026] Preferred combinations of metals in the fine metal particlesaccording to the invention include Au—Fe, Ag—Fe, Pd—Fe, Pt—Fe, Rh—Fe,Ru—Fe, Cu—Fe, Ni—Fe, Co—Fe, Sn—Fe, Ti—Fe, In—Fe, Al—Fe, Ta—Fe, Sb—Fe,and the like, and further include Au—Cu—Fe, Ag—Pt—Fe, Ag—Pd—Fe,Au—Pd—Fe, Au—Rh—Fe, Pt—Pd—Fe, Pt—Rh—Fe, Cu—Co—Fe, Ru—Ag—Fe, Ni—Pd—Fe,Au—Cu—Ag—Fe, Ag—Cu—Pt—Fe, Ag—Cu—Pd—Fe, Ag—Au—Pd—Fe, Au—Rh—Pd—Fe,Ag—Pt—Pd—Fe, Ag—Pt—Rh—Fe, Cu—Co—Pd—Fe, and the like.

[0027] The average particle diameter of the fine metal particlesaccording to the invention is in the range of from 1 to 200 nm,preferably from 2 to 70 nm. When the average particle diameter thereofis in the range of from 1 to 200nm, a conductive coating film havinghigh transparency can be obtained.

[0028] In case where the average particle diameter of the fine metalparticles exceeds 200 nm, light absorption by the metals is enhanced andthis makes the particle layer have a reduced light transmittance and anincreased haze. Because of this, when a substrate with such coating filmis used as the front panel of, e.g., a cathode ray tube, there are caseswhere the image produced has reduced resolution. In case where theaverage particle diameter of the fine metal particles is smaller than 1nm, the surface resistance of, the particle layer increases abruptly andthis may make it impossible to obtain a coating film having such a lowresistance value as to enable the objects of the invention to beaccomplished.

[0029] Furthermore, the content of iron in the fine metal particles isin the range of from 0.1 to 3.0% by weight, preferably from 0.2 to 2.0%by weight, based on the weight of the fine metal particles.

[0030] Fine metal particles containing iron in an amount within thatrange are capable of forming a transparent conductive fine-particlelayer which has even conductivity and low resistance and is excellent inscratch strength and durability.

[0031] In case where the content of iron in the fine metal particles islower than 0.1% by weight, an alloy-like property (the property of beingless susceptible to ionization as compared with the pure metal) is weak,so that the noniron metal cannot be sufficiently inhibited fromoxidizing or ionizing. There are hence cases where the fine metalparticles suffer particle growth, resulting in a decrease inconductivity or light transmittance.

[0032] Iron contents in the fine metal particles exceeding 3.0% byweight are undesirable in that conductivity may decrease considerablyalthough the degree of this conductivity decrease varies depending onthe kind of the noniron metal.

[0033] In another embodiment, the fine metal particles described abovemay be ones in which part of the surface thereof is in the form of anoxide and/or a hydroxide. These fine metal particles preferably are onesin which at least 25% of the surface is covered with an oxide and/or ahydroxide.

[0034] The fine metal particles covered with an oxide and/or a hydroxidein a degree within that range have high dispersibility. Because of this,a coating liquid having a long pot life can be obtained therefromwithout using an organic stabilizer. In case where the proportion of theoxide and/or hydroxide coating film on the surface of the fine metalparticles is lower than 25%, it is difficult to obtain a stablefine-metal-particle dispersion, or a coating liquid for formingtransparent conductive coating films which has a long pot life, withoutusing an organic stabilizer or the like. Fine metal particles in whichinner parts thereof have been oxidized into an oxide and/or hydroxideare undesirable in that they do not have improved stability but tend tohave reduced conductivity.

[0035] From the standpoint of dispersibility, the fine metal particlesaccording to the invention desirably are ones which give an aqueousdispersion which, when having a fine-particle concentration (percent byweight: the number of grams of fine metal particles in 100 g of thedispersion) of 0.5% by weight, has a flow electrical current potentialin the range of from 50 to 300 μeq/g, preferably from 60 to 200 μeq/g.When the flow electrical current potential thereof is in this range, thefine metal particles have excellent dispersion stability like colloidalmetal oxide particles, such as colloidal silica, and do not aggregate ina coating liquid. Consequently, a coating liquid for forming transparentconductive coating films which has a long pot life can be obtainedtherefrom without using a large amount of an organic stabilizer as incoating liquids containing fine metal particles heretofore in use. Finemetal particles for which the flow electrical current potential is lowerthan 50 μeq/g cannot give a stable fine-metal-particle dispersion, or acoating liquid for forming transparent conductive coating films having along pot life, without using an organic stabilizer or the like. In casewhere the flow electrical current potential is higher than 300 μeq/g,the fine metal particles tend to have reduced conductivity.

[0036] Flow electrical current potential is measured with a flowelectrical current potential meter (PCD 03PH, manufactured by Mutec) orthe like. This measurement of flow electrical current potential is madeon an aqueous dispersion having a fine-particle concentration of 0.5% byweight.

[0037] Such fine metal particles in which at least part of the surfaceof the fine metal particles is in the form of an oxide and/or hydroxideof the metals or such fine metal particles which give an aqueousdispersion which, when having a fine-particle concentration of 0.5% byweight, has a flow electrical current potential in the range of from 50to 300 μeq/g are inhibited from suffering metal oxidation in inner partsof the fine metal particles and from undergoing ionization and theresultant growth of fine metal particles. Such fine metal particleshence do not cause corrosion of the substrate or other materials.Because of this, the coating film suffers little decrease inconductivity or light transmittance and, as a result, a highly reliablesubstrate with transparent conductive coating film and a highly reliabledisplay device can be obtained. Furthermore, since these fine metalparticles are excellent in dispersibility and stability, the amount ofan organic stabilizer to be used can be reduced and the removal of theorganic stabilizer after coating film formation is easy. The organicstabilizer can hence be inhibited from remaining to impair conductivity.In addition, there is no need of burning the substrate at a temperatureas high as 400° C. or above after coating film formation in order toremove the organic stabilizer as in related-art techniques, and theorganic stabilizer can be removed at a low temperature. Consequently,not only the aggregation and/or fusion of fine metal particles whichoccurs in high-temperature burning can be prevented, but also thecoating film obtained can be prevented from having an impaired haze.

[0038] Since the fine metal particles according to the inventiondescribed above contain iron in a specific amount, they retain highconductivity and have strong alloy-like properties. Consequently, whenthe fine metal particles are used to form a conductive coating film, thenoniron metal can be inhibited from oxidizing or ionizing and particlegrowth is inhibited, whereby conductivity and light transmittance can beinhibited from decreasing. Furthermore, use of such fine metal particlesmakes it possible to obtain a stable fine-metal-particle dispersion or acoating liquid for forming transparent conductive coating films whichhas a long pot life.

[0039] The fine metal particles according to the invention can beproduced by a known method (see Physicochemical and Engineering Aspects109(1995) 55-62; NanoStructured Materials, Vol.7,No.6,pp.611-618(1996);or JP-A-10-188681 (corresponding to U.S. Pat. No. 6,136,228 and U.S.Pat. No. 6,180,030)), except that a salt of iron is used so as to obtainfine metal particles having an iron content of from 0.1 to 3.0% byweight. For example, the particles can be produced by the followingproduction process.

[0040] [Process for Producing Fine Metal Particles]

[0041] A salt of iron and a salt of one or more noniron metals arereduced in a solvent comprising water and/or an organic solvent in thepresence of a reducing agent in such a manner as to result in fine metalparticles having an iron content in the range of from 0.1 to 3.0% byweight. Specifically, examples of this process include the followingmethods (i) and (ii).

[0042] Method (i)

[0043] This method comprises simultaneously reducing a salt of iron anda salt of noniron metal in a solvent comprising water and/or an organicsolvent in the presence of a reducing agent.

[0044] Although the iron may be either ferric iron (trivalent) orferrous iron (bivalent), it is especially preferably ferric iron.

[0045] Examples of the salt of iron include salts such as iron chloride,iron nitrate, iron sulfate, and organic acid salts, e.g., iron acetate,and mixtures of there salts.

[0046] Examples of the salt of noniron metal include the chlorides,nitrates, sulfates, and organic acid salts, e.g., acetates, of metalssuch as Au, Ag, Pd, Pt, Rh, Ru, Cu, Ni, Co, Sn, Ti, In, Al, Ta, and Sband mixtures of these salts. Specific examples thereof includechloroauric acid, silver nitrate, palladium chloride, palladium nitrate,palladium acetate, ruthenium chloride, nickel chloride, nickel nitrate,copper nitrate, copper chloride, copper citrate, titanium tetrachloride,indium chloride, indium nitrate, and the like and mixtures of these. Theorganic acid salts herein include carboxylic acid salts, polycarboxylicacid salts, and the like.

[0047] In the solvent comprising water and/or an organic solvent, theconcentration of the salt of iron and the salt of noniron metal ispreferably in the range from 0.1 to 3.0% by weight, more preferably from0.2 to 2.0% by weight, in terms of total concentration of the metals(percent by weight: the number of grams of the metals in 100 g of thesolution).

[0048] As the organic solvent may be used alcohols such as4-hydroxy-4-methyl-2-pentanone and tetrahydrofuryl alcohol and etherssuch as propylene glycol monomethyl ether and diethylene glycolmonoethyl ether. In the invention, the solvent may consist of a singlesolvent or a mixture of two or more solvents, and may be a mixed solventcomposed of an organic solvent and water.

[0049] In case where the concentration of the salt of iron and the saltof noniron metal is lower than 0.1% by weight in terms of totalconcentration of the metals to be yielded, the rate of generation offine metal particles tends to be low or the fine metal particlesobtained tend to have uneven particle diameters. In addition, there arecases where the yield of fine metal particles is considerably low.

[0050] In case where the concentration of the salt of iron and the saltof noniron metal exceeds 3.0% by weight in terms of total concentrationof the metals, the reduction and precipitation of metal ions proceed tooquickly and this tends to give fine metal particles which have unevenparticle diameters or have aggregated.

[0051] Examples of the reducing agent include ferrous sulfate, ammoniumferrous sulfate, ferrous oxalate, trisodium citrate, tartaric acid,L(+)-ascorbic acid, sodium borohydride, sodium hypophosphite, and thelike. When sodium borohydride or sodium hypophosphite is used as areducing agent, B or P undesirably comes into the fine metal particles.However, use of an iron salt such as ferrous sulfate or ammonium ferroussulfate as a reducing agent can yield highly conductive fine metalparticles containing neither B nor P. In the invention, the salt of iron(ferric salt) to be used for constituting the fine metal particles forconstituting fine metal particles is distinctly distinguished from thesalt of iron (ferrous salt) to be used as a reducing agent. Almost allthe salt of iron used for constituting fine metal particles participatesin the constitution of fine metal particles, whereas the salt of ironused as a reducing agent hardly participates in the constitution of finemetal particles and is usually removed by an operation such as washing.However, the iron salt used as a reducing agent can also become, uponoxidation, one for constituting fine metal particles, although these twoiron salts should be distinctly distinguished as salts having differentfunctions.

[0052] The amount of the reducing agent to be used here is in the rangeof preferably from 0.1 to 5.0 mol, more preferably from 1.0 to 3.0 mol,per mol of the sum of the salt of iron and the salt of noniron metal. Aslong as the amount of the reducing agent is within this range, finemetal particles having high conductivity can be obtained in high yield.

[0053] In case where the amount of the reducing agent is smaller than0.1 mol per mol of the sum of the metal salts, the yield of fine metalparticles is reduced because of the insufficient reducing ability andthe fine metal particles obtained may have an iron content lower than0.1% by weight. Namely, there are cases where the effect of theiron-containing fine metal particles according to the invention is notobtained. Even when the amount of the reducing agent exceeds 5.0 mol permol of the sum of the metal salts, not only the yield is not improvedany more, but also fine metal particles containing B or P in a largeamount are obtained according to the kind of the reducing agent. Suchfine metal particles have insufficient conductivity.

[0054] Conditions for the reduction with such a reducing agent are notparticularly limited as long as the metal salts can be reduced. Thereduction may be accomplished by adding the reducing agent to the metalsalts prepared in the concentration shown above and optionally heatingor stirring the mixture according to need.

[0055] An organic stabilizer can be further used in the inventionaccording to need. Examples of the organic stabilizer include gelatin,poly(vinyl alcohol), poly(acrylic acid), hydroxypropyl cellulose,polycarboxylic acids such as oxalic acid, malonic acid, succinic acid,glutaric acid, adipic acid, sebacic acid, maleic acid, fumaric acid,phthalic acid, and citric acid and salts of these acids, heterocycliccompounds such as vinylpyrrolidone and polyvinylpyrrolidone, mixtures ofthese, and the like.

[0056] The timing of addition of the organic stabilizer is notparticularly limited, and the stabilizer may be added either before orsimultaneously with or after the addition of the reducing agent.

[0057] The amount of such an organic stabilizer to be used may be suchthat the organic stabilizer is contained in an amount of from 1 to 10mol, preferably from 2 to 8 mol, per mol of the fine metal particles tobe yielded.

[0058] In case where the amount of the organic stabilizer is less than 1mol/mol-metals, the fine metal particles obtained may have insufficientdispersibility and aggregate. In case where the amount thereof exceeds10 mol/mol-metals, the residual organic stabilizer may impairconductivity.

[0059] In this method of the invention, the dispersion of fine metalparticles thus obtained through reduction may be heat-treated accordingto need in a pressure vessel at a temperature of about 100° C. orhigher. This heat treatment yields fine metal particles having a moreeven particle diameter.

[0060] Besides method (i) described above, the following method (ii) canbe used to prepare fine metal particles.

[0061] Method (ii)

[0062] This method comprises treating a dispersion of fine iron metalparticles or fine particles of an iron-containing alloy by causing fineparticles or ions of a metal having a higher standard hydrogen electrodepotential than the fine iron metal particles or fine iron-containingalloy particles to be present in the dispersion to thereby deposit thenoniron metal having a higher standard hydrogen electrode potential onthe fine iron metal particles and/or fine iron-containing alloyparticles.

[0063] The dispersion of fine iron metal particles or fineiron-containing alloy particles to be used in method (ii) is notparticularly limited. However, a dispersion of fine particles of Fe,Ag—Pd—Fe, Ag—Fe, Ru—Fe, or the like may be used.

[0064] Such a dispersion can be prepared, for example, by reducing ametal salt of iron or a combination of a metal salt of iron with a saltof one or more noniron metals in the presence of a reducing agent. Usemay be made of the dispersion of fine iron-containing metal particlesprepared by method (i) described above.

[0065] In those fine metal particles, the difference in standardhydrogen electrode potential between the iron and the noniron metalwhich constitute the particles (the difference between the metal havinga higher standard hydrogen electrode potential and iron, when two ormore metals are contained) is desirably 0.05 eV or larger, preferably0.1 eV or larger. In these fine metal particles, the metal having thehighest standard hydrogen electrode potential is desirably present in anamount in the range of from 97 to 99.9% by weight based on the weight ofthe fine metal particles. When the content of the metal having thehighest standard hydrogen electrode potential is lower than 97% byweight or higher than 99.9% by weight, there are cases where the effectof inhibiting the fine metal particles from oxidizing or ionizing isinsufficient and no improvement in reliability is brought about.

[0066] This production method is suitable when the noniron metal is Au,Ag, Pd, Pt, Ph, Ru, Co, Sn, In, or the like.

[0067] As the reducing agent may be used those enumerated as examplesfor method (i) described above. Methods of reduction also are notparticularly limited, and the reduction may be conducted in the samemanner as that shown as an example for method (i) described above.

[0068] In method (ii) also , the organic stabilizers shown above may beused according to need, and the dispersion of fine metal particlesobtained through reduction may be heat-treated according to need in apressure vessel at a temperature of about 100° C. or higher.

[0069] The timing of addition of an organic stabilizer is notparticularly limited, and the stabilizer may be added either before orsimultaneously with or after the addition of the reducing agent.

[0070] Method (iii)

[0071] In the invention, an oxidizing agent may be subsequently added tothe dispersion of fine metal particles thus obtained to thereby oxidizeat least part of the surface of the fine metal particles (method (iii)).

[0072] This oxidation can yield fine metal particles whose surface is inthe form of an oxide and/or a hydroxide. The surface may be either anoxide or a hydroxide or may be one in which a hydroxide and an oxidecoexist.

[0073] As the oxidizing agent may be used, for example, oxygen, hydrogenperoxide, ozone, or the like.

[0074] The amount of the oxidizing agent to be added here, which variesdepending on the kind of the oxidizing agent, is not particularlylimited as long as at least part (about 25% or more) of the surface ofthe fine metal particles can be converted to an oxide and/or hydroxideof the metals. Specifically, the amount of the oxidizing agent may be inthe range of from 0.01 to 0.2 mol, preferably from 0.02 to 0.15 mol, permol of the sum of the metals.

[0075] In case where the amount of the oxidizing agent added is smallerthan 0.01 mol, about 25% or more of the surface of the fine metalparticles cannot be converted to an oxide and/or hydroxide of the metalsand the fine metal particles cannot have a flow electrical currentpotential in the range of from 50 to 300 μeq/g. Namely, it is difficultto obtain a transparent conductive coating liquid having sufficientdispersion stability and a long pot life. Moreover, there are caseswhere conductivity and light transmittance are impaired, making itimpossible to obtain a highly reliable substrate with conductive coatingfilm or a highly reliable display device.

[0076] In case where the amount of the oxidizing agent added exceeds 0.2mol there is a tendency for the fine metal particles to be oxidized notonly in the surface thereof but also in inner parts thereof. There arehence cases where conductivity decreases considerably.

[0077] Conditions for the oxidation also are not particularly limited,and treatments such as heating and stirring may be conducted accordingto need.

[0078] [Coating Liquid for Forming Transparent Conductive Coating Film]

[0079] Next, the coating liquid of the invention for forming transparentconductive coating films will be explained.

[0080] The coating liquid of the invention for forming transparentconductive coating films comprises the fine metal particles describedabove and a polar solvent.

[0081] In the coating liquid for forming transparent conductive coatingfilms, the fine metal particles are desirably contained in an amount offrom 0.05 to 5% by weight, preferably from 0.1 to 2% by weight, based onthe weight of the coating liquid.

[0082] Examples of the polar solvent to be used in the invention includewater; alcohols such as methanol, ethanol, propanol, butanol, diacetonealcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, ethylene glycol,and hexylene glycol; esters such as the methyl ester of acetic acid andethyl acetate ester; ethers such as diethyl ether, ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, diethylene glycol monomethyl ether, and diethyleneglycol monoethyl ether; ketones such as acetone, methyl ethyl ketone,acetylacetone, and acetoacetic acid esters; and the like. These may beused alone or as a mixture of two or more thereof.

[0083] This coating liquid for forming transparent conductive coatingfilms may contain conductive fine particles other than the fine metalparticles described above.

[0084] As the conductive fine particles other than the fine metalparticles can be used known ones such as fine particles of a transparentconductive inorganic oxide or a finely particulate carbon (seeJP-A-63-11519 and U.S. Pat. No. 6,136,228).

[0085] Examples of the fine particles of a transparent conductiveinorganic oxide include tin oxide, tin oxide doped with Sb, F, or P,indium oxide, indium oxide doped with Sn or F, antimony oxide, lowlyoxidized titanium, and the like.

[0086] The average particle diameter of those conductive fine particlesis desirably in the range of from 1 to 200 nm, preferably from 2 to 150nm.

[0087] Such conductive fine particles may be contained in an amount ofup to 4 parts by weight per part by weight of the fine metal particles.Amounts of the conductive fine particles exceeding 4 parts by weight areundesirable in that there are cases where conductivity is reduced toimpair the electromagnetic wave shielding effect.

[0088] Incorporation of such conductive fine particles enables formationof a transparent conductive fine-particle layer having bettertransparency than the transparent conductive fine-particle layerconstituted of fine metal particles alone. Furthermore, incorporation ofthe conductive fine particles enables the substrate with transparentconductive coating film to be produced at low cost.

[0089] A matrix ingredient serving as a binder for the fine metalparticles after coating film formation may be contained in the coatingliquid for forming transparent conductive coating films according to theinvention. This matrix ingredient preferably is one comprising silica.Examples of the matrix ingredient include products of hydrolyticpolycondensation of organosilicon compounds such as organosiliconcompounds, silicic acid polycondensates obtained by dealkalizing aqueoussolutions of alkali metal silicates, and resins for coating materials.The resins for coating materials may be either thermosetting resins orthermoplastic resins. Specific examples thereof include thermoplasticresins such as polyester resins, polycarbonate resins, polyamide resins,vinyl chloride resins, vinyl acetate resins, fluororesins, andthermoplastic acrylic resins, urethane resins, epoxy resins, melamineresins, butyral resins, phenolic resins, and the like. This matrix maybe contained in an amount of from 0.01 to 0.5 parts by weight,preferably from 0.03 to 0.3 parts by weight, per part by weight of thefine metal particles.

[0090] An organic stabilizer may be contained in the coating liquid forforming transparent conductive coating films in order to further improvethe dispersibility of the fine metal particles of the invention althoughit is not always necessary because the fine metal particles areexcellent in dispersibility and stability. Examples of this organicstabilizer include gelatin, poly(vinyl alcohol), polyvinylpyrrolidone,poly(acrylic acid), hydroxypropyl cellulose, polycarboxylic acids suchas oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid,sebacic acid, maleic acid, fumaric acid, phthalic acid, and citric acidand salts of these acids, heterocyclic compounds such asvinylpyrrolidone and polyvinylpyrrolidone, mixtures of these, and thelike.

[0091] This organic stabilizer may be contained in an amount of from0.005 to 0.5 parts by weight, preferably from 0.005 to 0.2 parts byweight, per part by weight of the fine metal particles. When the amountof the organic stabilizer is smaller than 0.005 parts by weight, thereare cases where sufficient dispersibility and stability cannot beobtained. Even when the amount thereof exceeds 0.5 parts by weight, notonly a further improvement in dispersibility or stability is not broughtabout, but also the organic stabilizer may remain in a larger amount toimpair conductivity.

[0092] When this coating liquid for forming transparent conductivecoating films is used, a transparent conductive fine-particle layerhaving a surface resistance of from 10² to 10⁴ Ω/▭ can be formed. Thisconductive layer is hence effective in shielding from electromagneticwaves and can effectively diminish the electromagnetic field produced bythe emission of electromagnetic waves.

[0093] In particular, the fine metal particles the surface of which hasbeen oxidized and which have a flow electrical current potential withina specific range are excellent in dispersibility and stability, and thecoating liquid for forming transparent conductive coating films whichcontains such fine metal particles has a long pot life. When thiscoating liquid for forming transparent conductive coating films is used,a substrate with transparent conductive coating films can be obtainedwhich is coated with a transparent conductive coating film excellent inconductivity and electromagnetic shielding properties and having highreliability. Furthermore, since these fine metal particles are excellentin dispersibility and stability, the amount of an organic stabilizer tobe used can be reduced. As a result, the removal of the organicstabilizer after coating film formation is easy, and conductivityimpairment by a residual organic stabilizer can be inhibited. Inaddition, there is no need of burning the substrate at a temperature ashigh as 400° C. or above after coating film formation in order to removethe organic stabilizer as in related-art techniques, and the organicstabilizer can be removed at a low temperature. Consequently, not onlythe aggregation or fusion of fine metal particles which occurs inhigh-temperature burning can be prevented, but also the coating filmobtained can be prevented from having an impaired haze.

[0094] [Substrate with Transparent Conductive Coating Film]

[0095] The substrate with transparent conductive coating film accordingto the invention will be explained below.

[0096] In the substrate with transparent conductive coating filmaccording to the invention, a transparent conductive fine-particle layercomprising the fine metal particles described above has been formed on asubstrate such as, e.g., a film, sheet, or another molding made of aglass, plastic, ceramic, or the like.

[0097] (Transparent Conductive Fine-Particle Layer)

[0098] The thickness of the transparent conductive fine-particle layeris desirably in the range of about from 5 to 200 nm, preferably from 10to 150 nm. As long as the thickness thereof is within this range, asubstrate with transparent conductive coating film which has anexcellent electromagnetic shielding effect can be obtained.

[0099] This transparent conductive fine-particle layer may containconductive fine particles other than the fine metal particles describedabove, a matrix ingredient, and an organic stabilizer according to need.Examples of these ingredients are the same as those shown above.

[0100] (Transparent Coating Film)

[0101] In the substrate with transparent conductive coating filmaccording to the invention, a transparent coating film having a lowerrefractive index than the transparent conductive fine-particle layer hasbeen formed on the transparent conductive fine-particle layer.

[0102] The thickness of the transparent coating film is desirably in therange of from 50 to 300 nm, preferably from 80 to 200 nm. The refractiveindex of the transparent coating film is regulated to a value usuallylower by about from 1.40 to 1.60 than the refractive index of theconductive fine-particle layer in order to impart anti-reflectionperformance.

[0103] This transparent coating film is formed, for example, from aninorganic oxide such as silica, titania, or zirconia or a compositeoxide of them. Especially preferred for use as the transparent coatingfilm in the invention is a silica-based coating film comprising aproduct of hydrolytic polycondensation of a hydrolyzable organosiliconcompound or comprising a silicic acid polycondensate obtained bydealkalizing an aqueous solution of an alkali metal silicate. Thesubstrate with transparent conductive coating film which has such atransparent coating film has excellent anti-reflection properties.

[0104] Additive such as fine particles constituted of alow-refractive-index material, e.g., magnesium fluoride, dyes, andpigments may be contained in the transparent coating film according toneed.

[0105] (Process for Producing Substrate with TransparentConductive-Coating Film)

[0106] The substrate with transparent conductive coating film accordingto the invention can be produced in the following manner.

[0107] (Formation of Transparent Conductive Fine-Particle Layer)

[0108] First, a coating liquid for forming transparent conductivecoating films which comprises fine metal particles having an averageparticle diameter of from 1 to 200 nm and a polar solvent is applied toa substrate and dried to form a transparent conductive fine-particlelayer.

[0109] The coating liquid for forming transparent conductive coatingfilms to be used here comprises fine metal particles and a polarsolvent. Examples of the fine metal particles and the polar solvent arethe same as those shown above.

[0110] The fine metal particles are contained in the coating liquid forforming transparent conductive coating films desirably in an amount offrom 0.05 to 5% by weight, preferably from 0.1 to 2% by weight, based onthe weight of coating liquid.

[0111] Conductive fine particles other than the fine metal particles mayhave been added to this coating liquid for forming transparentconductive coating films. Examples of these conductive fine particlesare the same as those shown above.

[0112] For forming the transparent conductive fine-particle layer, usemay be made, for example, of a method which comprises applying thecoating liquid for forming transparent conductive coating films to asubstrate by a technique such as dipping, spinner coating, spraying,roll coating, or flexography and then drying the coating liquid at atemperature in the range of from ordinary temperature to about 90° C.

[0113] In the case where the coating liquid for forming transparentconductive coating films contains a matrix ingredient such as thoseshown above, a treatment for curing the matrix ingredient may beperformed.

[0114] Examples of the curing treatment include techniques which havebeen known, such as thermal curing, electromagnetic wave irradiation,and curing with a gas such as ammonia gas.

[0115] The thickness of the transparent conductive fine-particle layerformed by the method described above is preferably in the range of aboutfrom 50 to 200 nm. As long as the thickness thereof is within thisrange, a substrate with transparent conductive coating film which has anexcellent electromagnetic shielding effect can be obtained.

[0116] (Formation of Transparent Coating Film)

[0117] A coating liquid for transparent coating film formation issubsequently applied on the fine-particle layer to form, on thetransparent conductive fine-particle layer, a transparent coating filmhaving a lower refractive index than the fine-particle layer.

[0118] The thickness of the transparent coating film is desirably in therange of from 50 to 300 nm, preferably from 80 to 200 nm. When thethickness thereof is within this range, the coating film exhibitsexcellent anti-reflection properties. Methods for forming thetransparent coating film are not particularly limited, and use may bemade of a dry technique for thin film deposition, such as vacuumevaporation, sputtering, or ion plating, or a wet technique for thinfilm formation, such as dipping, spinner coating, spraying, rollcoating, or flexography as mentioned above, according to the material ofthis transparent coating film.

[0119] When the transparent coating film is formed by a wet techniquefor thin film deposition, use can be made of a coating liquid fortransparent coating film formation which has been known (seeJP-A-10-188681 (corresponding to U.S. Pat. No. 6,136,228)). As such acoating liquid for transparent coating film formation may be used, forexample, a coating liquid which contains an inorganic oxide such assilica, titania, or zirconia or a composite oxide of them as aningredient for transparent coating film formation.

[0120] Preferred for use as the coating liquid for transparent coatingfilm formation in the invention is a silica-based coating liquid fortransparent coating film formation which contains either a product ofhydrolytic polycondensation of a hydrolyzable organosilicon compound ora silicic acid solution obtained by dealkalizing an aqueous solution ofan alkali metal silicate. Especially preferred is one containing aproduct of hydrolytic polycondensation of an organosilicon compoundrepresented by the following general formula [1]. The silica-basedcoating film formed from this coating liquid has a lower refractiveindex than the conductive fine-particle layer comprising fine metalparticles, and the substrate with transparent coating film obtained hasexcellent anti-reflection properties.

R_(a)Si (OR′)_(4-a)  [1]

[0121] (In the formula, R is a vinyl group; aryl group, acrylic group,alkyl group having 1 to 8 carbon atoms, hydrogen atom, or halogen atom;R′ is a vinyl group, aryl group, acrylic group, alkyl group having 1 to8 carbon atoms, —C₂H₄OC_(n)H_(2n+1) (n is 1 to 4), or hydrogen atom; anda is an integer of 0 to 3.)

[0122] Examples of this organosilicon compound includetetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane,tetrabutoxysilane, tetraoctylsilane, methyltrimethoxysilane,methyltriethoxysilane, ethyltriethoxysilane, methyltriisopropoxysilane,vinyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane,and the like.

[0123] One or more of those organosilicon compounds are hydrolyzed, forexample, in a water/alcohol mixed solvent in the presence of an acidcatalyst. Thus, a coating liquid for transparent coating film formationwhich contains a product of hydrolytic polycondensation of theorganosilicon compounds is obtained. The concentration of thefilm-forming ingredient in this coating liquid (percent by weight: thenumber of grams of the film-forming ingredient in 100 g of the coatingliquid) is preferably from 0.5 to 2.0% by weight in terms of oxideamount.

[0124] The coating liquid for transparent coating film formation to beused in the invention may further contain fine particles constituted ofa low-refractive-index material, e.g., magnesium fluoride, conductivefine particles whose amount is small so as not to impair thetransparency and anti-reflection performance of the transparent coatingfilm, and/or additives such as a dye or pigment.

[0125] In the invention, the coating film formed by applying the coatingliquid for transparent coating film formation may be heated to 150° C.or higher during drying or after drying. Alternatively, the uncuredcoating film may be irradiated with an electromagnetic wave having ashorter wavelength than visible rays, such as ultraviolet, electronbeams, X-rays, or gamma-rays, or may be exposed to, an active gasatmosphere such as ammonia. This treatment promotes the curing of thefilm-forming ingredient to give a transparent coating film havingenhanced hardness.

[0126] Furthermore, the film formation through application of thecoating liquid for transparent coating film formation may be conductedin such a manner that the coating liquid for transparent coating filmformation is applied while keeping the transparent conductivefine-particle layer at about from 40 to 90° C. and the transparentcoating film is subjected to the treatments shown above (drying,heating, and curing). As a result, an antiglare substrate withtransparent coating film and reduced glaringness is obtained which hasring-like protrusions and recesses formed on the surface of thetransparent coating film.

[0127] [Display Device]

[0128] The substrate with transparent conductive coating film accordingto the invention has a transparent conductive fine-particle comprisingspecific fine metal particles. Because of this, the coated substrate hasa surface resistance in the range of from 10² to 10⁴ Ω/▭, which isrequired for electromagnetic shielding, and has satisfactoryanti-reflection performance in the visible ray region and near infraredregion. This substrate with transparent conductive coating film issuitable for use as the front panel of a display device.

[0129] The display device according to the invention is a device whichelectrically produces images thereon, such as a cathode ray tube (CRT),fluorescent character display tube (FIP), plasma display (PDP), orliquid-crystal display (LCD), and is provided with a front panelcomprising the substrate with transparent conductive coating filmdescribed above.

[0130] It is known that when display devices provided with conventionalfront panels are operated, electromagnetic waves are emitted from thefront panels simultaneously with image production on the front panels.The display device according to the invention can shield from suchelectromagnetic waves and effectively diminish the electromagnetic fieldinduced by the emission of such electromagnetic waves, because the frontpanel thereof comprises the substrate with transparent conductivecoating film which has a surface resistance of from 10² to 10⁴ Ω/▭.

[0131] When a light reflection occurs on the front panel of a displaydevice, the reflected light makes it difficult to see the imageproduced. However, in the display device according to the invention,such light reflections can be effectively prevented because the frontpanel comprises the substrate with transparent conductive coating film,which has sufficient anti-reflection performance in the visible rayregion and near infrared region.

[0132] Furthermore, in the case of a cathode ray tube in which the frontpanel thereof comprises the substrate with transparent conductivecoating film according to the invention and a small amount of a dye orpigment is contained in at least either of the layers constituting thetransparent conductive coating film, i.e., the transparent conductivefine-particle layer and the overlying transparent coating film, the dyeor pigment absorbs light having specific wavelengths. Thus, the contrastof images produced on the cathode ray tube can be improved.

EXAMPLES

[0133] The invention will be illustrated with reference to Examples, butthe invention should not be construed as being limited to theseExamples.

Example 1

[0134] To 100 g of pure water were added 9.6 g (3.6×10⁻² mol) ofpalladium nitrate dihydrate and 0.1 g of iron citrate (FeC₆H₅O₇:4.14×10⁻⁴ mol) so as to result in the proportion by weight in terms ofmetal shown in Table 1. Thus, an aqueous solution of mixed metal saltswas prepared. Subsequently, 200 g (0.218 mol: 6 mol/mol-metals) of anaqueous trisodium citrate solution was added as a stabilizer to thisaqueous solution of mixed metal salts. Thereto was then added 81.2 g(7.3×10⁻² mol: 2 mol/mol-metals) of an aqueous solution containingferrous sulfate in a concentration of 25% by weight as a reducing agent.This mixture was stirred at a temperature of 20° C. in a nitrogenatmosphere for 20 hours to prepare a dispersion of fine metal particles(P-1).

[0135] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight (for desalting) andthen dispersed in pure water to prepare an aqueous dispersion containingthe fine metal particles (P-1) in a concentration of 2.5% by weight interms of metal.

[0136] Subsequently, the aqueous dispersion of the fine metal particles(P-1) was treated with Nanomizer System (Nanomizer Co.: LA-33-S) toprepare an aqueous monodisperse dispersion of the fine metal particles(P-1) (dispersion in which the fine metal particles were dispersed inthe aqueous dispersion medium without aggregating or precipitating).This dispersion was placed in a sealed vessel (rotary evaporator) theatmosphere in which had been replaced with nitrogen gas. The water wasreplaced with 4-hydroxy-4-methyl-2-pentanone. Thus, a4-hydroxy-4-methyl-2-pentanone dispersion containing the fine metalparticles (P-1) in a concentration of 4.0% by weight was prepared.

[0137] The fine metal particles (P-1) obtained were evaluated foraverage particle diameter after the Nanomizer treatment and for flowelectrical current potential before the Nanomizer treatment. The resultsare shown in Table 1.

[0138] The average particle diameter of the fine metal particles wasevaluated with a Microtrac particle size analyzer (9340-UPA,manufactured by Nikkiso Co., Ltd.). Flow electrical current potentialwas determined by diluting the aqueous dispersion containing fine metalparticles (P-1) in a concentration of 2.5% by weight to 0.5% by weightand titrating the diluted dispersion with a titrant (0.001 N Poly-Dadmacsolution, manufactured by Metron) using a flow electrical currentpotential meter (PCD-03-PH, manufactured by Mutec).

EXAMPLE 2

[0139] To 100 g of pure water were added 6.12 g (3.6×10⁻² mol) of anaqueous silver nitrate solution and 0.1 g (4.2×10⁻⁴ mol) of an aqueousiron citrate solution so as to result in the proportion by weight interms of metal shown in Table 1. Thus, an aqueous solution of mixedmetal salts was prepared. Subsequently, 200 g (0.219 mol: 6mol/mol-metals) of trisodium citrate having a concentration of 30% byweight was added as a stabilizer to this aqueous solution of mixed metalsalts. Thereto was then added 76.5 g (3.64×10⁻² mol/mol-metals) of anaqueous solution containing ferrous sulfate in a concentration of 25% byweight as a reducing agent. This mixture was stirred at a temperature of20° C. in a nitrogen atmosphere for 20 hours to prepare a dispersion offine metal particles (P-2).

[0140] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-2) in a concentration of 2.5% by weight in terms of metal.

[0141] Subsequently, the aqueous dispersion of the fine metal particles(P-2) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-2). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the fine metal particles (P-2) in a concentrationof 4.0% by weight was prepared.

[0142] The fine metal particles (P-2) obtained were evaluated foraverage particle diameter and flow electrical current potential in thesame manners as in Example 1. The results are shown in Table 1.

Example 3

[0143] To 100 g of pure water were added 8.53 g (3.2×10⁻² mol) ofpalladium nitrate dihydrate, 0.34 g (0.2×10⁻² mol) of silver nitrate,and 0.094 g (3.91×10⁻⁴ mol) of an aqueous iron citrate solution so as toresult in the proportion by weight in terms of metal shown in Table 1.Thus, an aqueous solution of mixed metal salts was prepared.Subsequently, 189 g (0.206 mol: 6 mol/mol-metals) of an aqueous solutioncontaining trisodium citrate in a concentration of 30% by weight wasadded as a stabilizer to this aqueous solution of mixed metal salts.Thereto was then added 76.5 g (6.88×10⁻² mol: 2 mol/mol-metals) of anaqueous solution containing ferrous sulfate in a concentration of 25% byweight as a reducing agent. This mixture was stirred at a temperature of20° C. in a nitrogen atmosphere for 20 hours to prepare a dispersion offine metal particles (P-3).

[0144] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-3) in a concentration of 2.5% by weight in terms of metal.

[0145] Subsequently, the aqueous dispersion of the fine metal particles(P-3) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-3). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the fine metal particles (P-3) in a concentrationof 4.0% by weight was prepared.

[0146] The fine metal particles (P-3) obtained were evaluated foraverage particle diameter and flow electrical current potential in thesame manners as in Example 1. The results are shown in Table 1.

Example 4

[0147] To 100 g of pure water were added 9.6 g (3.6×10⁻² mol) ofpalladium nitrate dihydrate and 0.165 g (6.87×10⁻⁴ mol) of an aqueousiron citrate solution so as to result in the proportion by weight interms of metal shown in Table 1. Thus, an aqueous solution of mixedmetal salts was prepared. Subsequently, 202 g (0.22 mol: 6mol/mol-metals) of trisodium citrate having a concentration of 30% byweight was added as a stabilizer to this aqueous solution of mixed metalsalts. Thereto was then added 81.6 g (7.34×10⁻² mol: 2 mol/mol-metals)of an aqueous solution containing ferrous sulfate in a concentration of25% by weight as a reducing agent. This mixture was stirred at atemperature of 20° C. in a nitrogen atmosphere for 20 hours to prepare adispersion of fine metal particles (P-4).

[0148] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-4) in a concentration of 2.5% by weight in terms of metal.

[0149] Subsequently, the aqueous dispersion of the fine metal particles(P-4) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-4). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, oxygen was forced thereintoas an oxidizing agent in an amount of 0.02 mol per mol of the fine metalparticles (sum of the metals) to prepare, with stirring, an aqueousdispersion containing fine metal particles (P-4) in a concentration of2.5% by weight in which the surface of the fine metal particles (P-4)was partly in the form of an oxide and/or a hydroxide.

[0150] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-4) in a concentration of 4.0% by weight was prepared.

[0151] The fine metal particles (P-4) obtained were evaluated foraverage particle diameter and flow electrical current potential withrespect to the aqueous dispersion after oxidation. The results are shownin Table 1.

Example 5

[0152] An aqueous; dispersion containing fine metal particles (P-1) in aconcentration of 2.5% by weight in terms of metal was prepared in thesame manner as in Example 1.

[0153] Subsequently, the aqueous dispersion of the fine metal particles(P-1) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-1). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, oxygen was forced thereintoas an oxidizing agent in an amount of 0.1 mol per mol of the fine metalparticles (sum of the metals) to prepare, with stirring, an aqueousdispersion containing fine metal particles (P-5) in a concentration of2.5% by weight in which the surface of the fine metal particles (P-1)was partly in the form of an oxide and/or a hydroxide.

[0154] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-5) in a concentration of 4.0% by weight was prepared.

[0155] The fine metal particles (P-5) obtained were evaluated foraverage particle diameter and flow electrical current potential withrespect to the aqueous dispersion after oxidation. The results are shownin Table 1.

Example 6

[0156] To 100 g of pure water were added 9.6 g (3.6×10⁻² mol) ofpalladium nitrate dihydrate and 0.184 g (7.63×10⁻⁴ mol) of iron citrateso as to result in the proportion by weight in terms of metal shown inTable 1. Thus, an aqueous solution of mixed metal salts was prepared.Subsequently, 203 g (0.221 mol: 6 mol/mol-metals) of an aqueous solutioncontaining trisodium citrate in a concentration of 30% by weight wasadded as a stabilizer to this aqueous solution of mixed metal salts.Thereto was then added 81.8 g (7.35×10⁻² mol: 2 mol/mol-metals) of anaqueous solution containing ferrous sulfate in a concentration of 25% byweight as a reducing agent. This mixture was stirred at a temperature of20° C. in a nitrogen atmosphere for 20 hours to prepare a dispersion offine metal particles (P-6).

[0157] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-6) in a concentration of 2.5% by weight in terms of metal.

[0158] Subsequently, the aqueous dispersion of the fine metal particles(P-6) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-6). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, oxygen was forced thereintoas an oxidizing agent in an amount of 0.02 mol per mol of the fine metalparticles (sum of the metals) to prepare, with stirring, an aqueousdispersion containing fine metal particles (P-6) in a concentration of2.5% by weight in which the surface of the fine metal particles (P-6)was partly in the form of an oxide and/or a hydroxide.

[0159] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-6) in a concentration of 4.0% by weight was prepared.

[0160] The fine metal particles (P-6) obtained were evaluated foraverage particle diameter and flow electrical current potential withrespect to the aqueous dispersion after oxidation. The results are shownin Table 1.

Example 7

[0161] An aqueous dispersion containing fine metal particles (P-2) in aconcentration of 2.5% by weight in terms of metal concentration wasprepared in the same manner as in Example 2.

[0162] Subsequently, the aqueous dispersion of the fine metal particles(P-2) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-2). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, an aqueous hydrogenperoxide solution was charged thereinto as an oxidizing agent in anamount of 0.01 mol per mol of the sum of the metals of the fine metalparticles to prepare, with stirring, an aqueous dispersion containingfine metal particles (P-7) in a concentration of 2.5% by weight in whichthe surface of the fine metal particles (P-2) was partly in the form ofan oxide and/or a hydroxide.

[0163] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-7) in a concentration of 4.0% by weight was prepared.

[0164] The fine metal particles (P-7) obtained were evaluated foraverage particle diameter and flow electrical current potential withrespect to the aqueous dispersion after oxidation. The results are shownin Table 1.

Example 8

[0165] An aqueous dispersion containing fine metal particles (P-8) in aconcentration of 2.5% by weight was prepared in the same manner as inExample 7,except that the aqueous hydrogen peroxide solution asoxidizing agent was used in an amount of 0.02 mol per mol of the sum ofthe metals of the fine metal particles.

[0166] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-8) in a concentration of 4.0% by weight was prepared.

[0167] The partly surface-oxidized fine metal particles (P-8) obtainedwere evaluated for average particle diameter and flow electrical currentpotential with respect to the aqueous dispersion after oxidation. Theresults are shown in Table 1.

Example 9

[0168] To 100 g of pure water were added 8.77 g (3.6×10⁻² mol) ofruthenium chloride dihydrate and 0.091 g (3.77×10⁻⁴ mol) of iron citrateso as to result in the proportion by weight in terms of metal shown inTable 1. Thus, an aqueous solution of mixed metal salts was prepared.Subsequently, 200 g (0.218 mol: 6 mol/mol-metals) of an aqueous solutioncontaining trisodium citrate in a concentration of 30% by weight wasadded as a stabilizer to this aqueous solution of mixed metal salts.Thereto was then added 43.8 g (0.362 mol: 10 mol/mol-metals) of anaqueous solution containing sodium borohydride in a concentration of 25%by weight as a reducing agent. This mixture was stirred at a temperatureof 20° C. in a nitrogen atmosphere for 1 hour to prepare a dispersion offine metal particles (P-9).

[0169] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-9) in a concentration of 2.5% by weight in terms of metal.

[0170] Subsequently, the aqueous dispersion of the fine metal particles(P-9) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-9). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, an aqueous hydrogenperoxide solution was charged thereinto in an amount of 0.02 mol per molof the sum of the metals of the fine metal particles to prepare, withstirring, an aqueous dispersion containing fine metal particles (P-9) ina concentration of 2.5% by weight in which the surface of the fine metalparticles (P-9) was partly in the form of an oxide and/or a hydroxide.

[0171] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-9) in a concentration of 4.0% by weight was prepared. The fine metalparticles (P-9) obtained were evaluated for average particle diameterand flow electrical current potential with respect to the aqueousdispersion after oxidation. The results are shown in Table 1.

COMPARATIVE EXAMPLE 1

[0172] To 100 g of pure water was added 9.6 g (3.6×10⁻² mol) ofpalladium nitrate dihydrate to prepare an aqueous metal salt solution.Subsequently, 198 g (0.216 mol: 6 mol/mol-metals) of trisodium citratehaving a concentration of 30% by weight was added as a stabilizer tothis aqueous solution. Thereto was then added 80 g (7.2×10⁻² mol: 2mol/mol-metal) of an aqueous solution containing ferrous sulfate in aconcentration of 25% by weight as a reducing agent. This mixture wasstirred at a temperature of 20° C. in a nitrogen atmosphere for 20 hoursto prepare a dispersion of fine metal particles (P-10).

[0173] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-10) in a concentration of 2.5% by weight in terms of metal.

[0174] Subsequently, the aqueous dispersion of the fine metal particles(P-10) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-10). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. The water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the fine metal particles (P-10) in a concentrationof 4.0% by weight was prepared.

[0175] The fine metal particles (P-10) obtained were evaluated foraverage particle diameter and flow electrical current potential in thesame manners as in Example 1. The results are shown in Table 1. Theaverage particle diameter was large as compared with the particlediameter of 5 μm which was separately determined after the Nanomizertreatment from a TEM photograph. The fine metal particles hadaggregated.

COMPARATIVE EXAMPLE 2

[0176] An aqueous dispersion containing fine metal particles (P-10) in aconcentration of 2.5% by weight in terms of metal was prepared in thesame manner as in Comparative Example 1.

[0177] Subsequently, the aqueous dispersion of the fine metal particles(P-10) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-10). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, oxygen was forced thereintoin an amount of 0.02 mol per mol of the sum of the metal of the finemetal particles to prepare, with stirring, an aqueous dispersioncontaining fine metal particles (P-11) in a concentration of 2.5% byweight in which the surface of the fine metal particles (P-10) waspartly in the form of an oxide and/or a hydroxide.

[0178] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-11) in a concentration of 4.0% by weight was prepared.

[0179] The fine metal particles (P-11) obtained were evaluated foraverage particle diameter and flow electrical current potential in thesame manners as in Example 1. The results are shown in Table 1. Theaverage particle diameter was large as compared with the particlediameter of 5 μm which was separately determined after the Nanomizertreatment from a TEM photograph. The fine metal particles hadaggregated.

COMPARATIVE EXAMPLE 3

[0180] To 100 g of pure water were added 9.6 g (3.6×10⁻² mol) ofpalladium nitrate dihydrate and 0.79 g (3.23×10⁻³ mol) of iron citrateso as to result in the proportion by weight in terms of metal shown inTable 1. Thus, an aqueous solution of mixed metal salts was prepared.Subsequently, 216 g (0.235 mol: 6 mol/mol-metals) of an aqueous solutioncontaining trisodium citrate in a concentration of 30% by weight wasadded as a stabilizer to this aqueous solution of mixed metal salts.Thereto was then added 86.7 g (7.8×10⁻² mol: 2 mol/mol-metals) of anaqueous solution containing ferrous sulfate in a concentration of 25% byweight as a reducing agent. This mixture was stirred at a temperature of20° C. in a nitrogen atmosphere for 20 hours to prepare a dispersion offine metal particles (P-12).

[0181] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-12) in a concentration of 2.5% by weight in terms of metal.

[0182] Subsequently, the aqueous dispersion of the fine metal particles(P-12) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-12). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. The water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the fine metal particles (P-12) in a concentrationof 4.0% by weight was prepared.

[0183] The fine metal particles (P-12) obtained were evaluated foraverage particle diameter and flow electrical current potential in thesame manners as in Example 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 4

[0184] An aqueous dispersion containing fine metal particles (P-12) in aconcentration of 2.5% by weight in terms of metal was prepared in thesame manner as in Comparative Example 3.

[0185] Subsequently, the aqueous dispersion of the fine metal particles(P-12) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-12). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, oxygen was forced thereintoin an amount of 0.02 mol per mol of the sum of the metals of the finemetal particles to prepare, with stirring, an aqueous dispersioncontaining fine metal particles (P-13) in a concentration of 2.5% byweight in which the surface of the fine metal particles (P-12) waspartly in the form of an oxide and/or a hydroxide.

[0186] Subsequently, the water was replaced with-4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-13) in a concentration of 4.0% by weight was prepared.

[0187] The fine metal particles (P-13) obtained were evaluated foraverage particle diameter and flow electrical current potential withrespect to the aqueous dispersion after oxidation. The results are shownin Table 1.

COMPARATIVE EXAMPLE 5

[0188] To 100 g of pure water was added 6.1 g (3.6×10⁻² mol) of silvernitrate-to prepare an aqueous silver nitrate solution. Subsequently, 198g (0.216 mol: 6 mol/mol-metal) of an aqueous solution containingtrisodium citrate in a concentration of 30% by weight was added as astabilizer to this aqueous silver nitrate solution. Thereto was thenadded 80 g (7.2×10⁻² mol:2 mol/mol)-of an aqueous solution containingferrous sulfate in a concentration of 25% by weight as a reducing agent.This mixture was stirred at a temperature of 20° C. in a nitrogenatmosphere for 1 hour to prepare a dispersion of fine metal particles(P-14).

[0189] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-14) in a concentration of 2.5% by weight in terms of metal.

[0190] Subsequently, the aqueous dispersion of the fine metal particles(P-14) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-14). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, oxygen was, forcedthereinto in an amount of 0.02 mol per mol of the metal of the finemetal particles to prepare, with stirring, an aqueous dispersion of finemetal particles (P-14) in which the surface of the fine metal particles(P-14) was partly in the form of an oxide and/or a hydroxide.

[0191] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-14) in a concentration of 4.0% by weight was prepared.

[0192] The fine metal particles (P-14) obtained were evaluated foraverage particle diameter and flow electrical current potential. Theresults are shown in Table 1.

COMPARATIVE EXAMPLE 6

[0193] To 100 g of pure water were added 6.1 g (3.6×10⁻² mol) of silvernitrate and 0.8 g (3.23×10⁻³ mol) of iron citrate so as to result in themetal proportion by weight shown in Table 1. Thus, an aqueous solutionof mixed metal salts was prepared. Subsequently, 216 g (0.236 mol: 6mol/mol-metals) of an aqueous solution containing trisodium citrate in aconcentration of 30% by weight was added as a stabilizer to this aqueoussolution of mixed metal salts. Thereto was then added 87 g (7. 85×10⁻²mol: 2 mol/mol-metals) of an aqueous solution containing ferrous sulfatein a concentration of 25% by weight as a reducing agent. This mixturewas stirred at a temperature of 20° C. in a nitrogen atmosphere for 1hour to prepare a dispersion of fine-metal particles (P-15).

[0194] From the dispersion obtained, the fine metal particles wereseparated and recovered with a centrifugal separator. These fine metalparticles were washed with 6.1 g of an aqueous solution containinghydrochloric acid in a concentration of 1% by weight and then dispersedin pure water to prepare an aqueous dispersion containing the fine metalparticles (P-15) in a concentration of 2.5% by weight in terms of metal.

[0195] Subsequently, the aqueous dispersion of the fine metal particles(P-15) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-15). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, oxygen was forced thereintoin an amount of 0.02 mol per mol of the sum of the metals of the finemetal particles to prepare, with stirring, an aqueous dispersion of finemetal particles (P-15) in which the surface of the fine metal particles(P-15) was partly in the form of an oxide and/or a hydroxide.

[0196] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-15) in a concentration of 4.0% by weight was prepared.

[0197] The fine metal particles (P-15) obtained were evaluated foraverage particle diameter and flow electrical current potential. Theresults are shown in Table 1. The average particle diameter was large ascompared with the particle diameter of 6 μm which was separatelydetermined after the Nanomizer treatment from a TEM photograph. The finemetal particles had aggregated.

COMPARATIVE EXAMPLE 7

[0198] An aqueous dispersion containing fine metal particles (P-12) in aconcentration of 2.5% by weight in terms of metal was prepared in thesame manner as in Comparative Example 3.

[0199] Subsequently, the aqueous dispersion of the fine metal particles(P-12) was treated with Nanomizer System to prepare an aqueousmonodisperse dispersion of the fine metal particles (P-12). Thisdispersion was placed in a rotary evaporator the atmosphere in which hadbeen replaced with nitrogen gas. Thereafter, oxygen was forced thereintoin an amount of 0.4mol per mol of the sum of the metals of the finemetal particles to prepare, with stirring, an aqueous dispersion of finemetal particles (P-16) in which the surface of the fine metal particles(P-12) was partly in the form of an oxide and/or a hydroxide.

[0200] Subsequently, the water was replaced with4-hydroxy-4-methyl-2-pentanone. Thus, a 4-hydroxy-4-methyl-2-pentanonedispersion containing the partly surface-oxidized fine metal particles(P-16) in a concentration of 4.0% by weight was prepared.

[0201] The fine metal particles (P-16), obtained were evaluated foraverage particle diameter and flow electrical current potential. Theresults are shown in Table 1. The average particle diameter was large ascompared with the particle diameter of 5 μm which was separatelydetermined after the Nanomizer treatment from a TEM photograph. The finemetal particles had aggregated. TABLE 1 Oxidizing Composition of agentComposition of Flow metal salt Reducing agent Amount fine metalparticles Average electrical Fine solution prepared Amount mol/ yieldedParticle current particles Fe Ag Pd Ru mol/mol- mol- Fe Ag Pd Rudiameter potential No. wt % wt % wt % wt % Kind metal Kind metal wt % wt% wt % wt % nm μeq/g Ex. 1 P-1 0.6 — 99.4 — ferrous 2 — — 0.5 — 99.5 — 4100 iron Ex. 2 P-2 0.6 99.4 — — ferrous 1 — — 0.5 99.5 — — 5 80 iron Ex.3 P-3 0.6 9.9 89.5 — ferrous 2 — — 0.5  9.9 89.6 — 4 90 iron Ex. 4 P-40.1 — 99.9 — ferrous 2 O₂ 0.02 0.1 — 99.9 — 5 120 iron Ex. 5 P-5 0.6 —99.4 — ferrous 2 O₂ 0.1  0.5 — 99.5 — 5 180 iron Ex. 6 P-6 1.1 — 98.9 —ferrous 2 O₂ 0.02 1.0 — 99.0 — 5 200 iron Ex. 7 P-7 0.6 99.4 — — ferrous1 H₂O₂ 0.01 0.5 99.5 — — 7 170 iron Ex. 8 P-8 0.6 99.4 — — ferrous 1H₂O₂ 0.02 0.5 99.5 — — 10 180 iron Ex. 9 P-9 0.6 — — 99.4 sodium 10 H₂O₂0.02 0.5 — — 99.5 15 180 boro- hydride Comp. P-10 — — 100 — ferrous 2 —— 0.05 — 99.95 — 300 40 Ex. 1 iron Comp. P-11 — — 100 — ferrous 2 O₂0.02 0.05 — 99.95 — 200 40 Ex. 2 iron Comp. P-12 4.5 — 95.5 — ferrous 2— — 4.00 — 96.0 — 4 260 Ex. 3 iron Comp. P-13 4.5 — 95.5 — ferrous 2 O₂0.02 4.00 — 96.0 — 5 280 Ex. 4 iron Comp. P-14 — 100 — — ferrous 2 O₂0.02 0.05 99.5 — — 5 50 Ex. 5 iron Comp. P-15 4.5 95.5 — — ferrous 2 O₂0.02 4.00 96.0 — — 250 40 Ex. 6 iron Comp. P-16 4.5 — 95.5 — ferrous 2O₂ 0.4  4.00 — 96.0 — 500 30 Ex. 7 iron

Examples 10 TO 18 AND COMPARATIVE EXAMPLES 8 TO 14 a) Preparation ofMatrix-Forming Ingredient Liquid (M)

[0202] A mixed solution consisting of 50 g of ethyl orthosilicate (SiO₂:28% by weight), 194.6 g of ethanol, 1.4 g of concentrated nitric acid,and 34 g of pure water was stirred at room temperature for 5 hours toobtain a liquid (M) containing a matrix-forming ingredient in an SiO₂concentration of 5% by weight.

b) Preparation of Coating Liquids for Forming Transparent ConductiveCoating Film

[0203] Seven parts by weight of each of the4-hydroxy-4-methyl-2-pentanone dispersions (P-1) to (P-16) shown inTable 1 was mixed with 1.1 part by weight of the matrix-formingingredient liquid (M), 81.9 parts by weight of ethanol, 10 parts byweight of butyl Cellosolve, and 0.005 parts by weight of citric acid.Thus, coating liquids for transparent conductive coating film formation(C-1) to (C-16) each having a solid concentration of 0.335% by weightwere prepared.

[0204] [Evaluation of Coating Liquid Stability]

[0205] Each of the coating liquids for transparent conductive coatingfilm formation was held at 50C for 24 hours and then examined for aprecipitate. The coating liquids which had no precipitate were examinedfor particle size distribution with a Microtrac particle size analyzer(9340-UPA, manufactured by Nikkiso Co., Ltd.). Stability was evaluatedbased on the following criteria. The results are shown in Table 2.

[0206] Evaluation Criteria:

[0207] No precipitate and no change in particle diameter: ⊚

[0208] No precipitate, slight change in particle diameter: ∘

[0209] No precipitate, considerable change in particle diameter: Δ

[0210] Precipitate observed: X

c) Preparation of Coating Liquid for Forming Transparent Coating Film

[0211] An ethanol/butanol/diacetone alcohol/isopropanol (2:1:1:5 byweight) mixed solvent was added to the matrix-forming ingredient liquid(M) to prepare a coating liquid for transparent coating film formationhaving an SiO₂ concentration of 1%-by weight.

d) Production of Panel Glasses with Transparent Conductive Coating Film

[0212] Each of the coating liquids for transparent conductive coatingfilm formation (C-1) to (C-16) was applied to a surface of a panel glass(14 inches) for cathode ray tubes by spinner coating while keeping thesurface at 40° C. under the conditions of 150 rpm and 90 seconds so asto give a transparent conductive coating film having a thickness of 20nm. Each coating liquid applied was dried.

[0213] Subsequently, the coating liquid for transparent coating filmformation was likewise applied on the transparent conductivefine-particle layers thus formed, by spinner coating under theconditions of 100 rpm and 90 seconds so as to give a transparent coatingfilm having a thickness of 100 nm. The coating liquid applied was driedand then burned at 160° C. for 30 minutes. Thus, substrates withtransparent conductive coating film were obtained.

[0214] The substrates with transparent conductive coating film obtainedwere subjected to the following evaluations.

[0215] [Surface Resistance, Haze, and Transmittance]

[0216] These substrates with transparent conductive coating film wereexamined for surface resistance with a surface resistance meter(LORESTA, manufactured by Mitsubishi Petrochemical Co., Ltd.) and forhaze with a haze computer (3000A, manufactured by Nippon Denshoku Co.,Ltd.).

[0217] Transmittance was measured with a spectrophotometer (HI-VISV-560,manufactured by Japan Spectroscopic Co., Ltd.).

[0218] [Scratch Strength (1)]

[0219] A standard test needle (manufactured by Rockwell Co., Ltd.;hardness, HRC-60; φ=0.5 mm) was set on the transparent coating film ofeach substrate with transparent conductive coating film. A load of 1 kgwas applied thereto and the needle was moved in a stroke of 30 to 40 mm.Thereafter, the coating film surface was visually examined from adistance of 45 cm while illuminating the surface at 1,000 lx.

[0220] No scratch mark was observed: ⊚

[0221] Reflection color changed (from purple to red) in fluorescentlight: ∘

[0222] No reflection color in fluorescent light, and scratch mark wasobserved: Δ

[0223] Base (glass substrate) was seen through: X

[0224] [Durability]

[0225] Durability was evaluated with respect to the following items (1)to (4).

[0226] (1) Color Change (HCl)

[0227] The substrates with transparent conductive coating film obtainedabove were immersed for 72 hours in an aqueous solution containing HClin a concentration of 10% by weight and then examined for transmittance.This transmittance was compared with the transmittance before thetreatment, and the color change was evaluated based on the followingcriteria.

Transmittance change (%)={(transmittance beforetreatment)−(transmittance after treatment)}/(transmittance beforetreatment)

[0228] Transmittance change, from 0 to less than 1%: ∘

[0229] Transmittance change, from 1 to less than 5%: Δ

[0230] Transmittance change, 5% or more: X

[0231] (2) Color Change (H₂O₂)

[0232] The substrates with transparent conductive coating film obtainedabove were immersed for 72 hours in an aqueous solution containing H₂O₂in a concentration of 10% by weight and then examined for transmittance.This transmittance was compared with the transmittance before thetreatment, and the color change was evaluated based on the same criteriaas shown above.

[0233] (3) Scratch Strength (2)

[0234] The coated substrates were treated in the same manner as in theColor Change (H₂O₂) and then examined for scratch strength.

[0235] (4) Surface Resistance (2)

[0236] The coated substrates were treated in the same manner as in theColor Change (H₂O₂) and then examined for surface resistance.

[0237] The results are shown together in Table 2. TABLE 2 Substrate withtransparent conductive coating film Durability Stability Surface SurfaceColor of coating resistivity Scratch resistance change Scratch liquid(Ω/□) transmittance % Haze % strength (Ω/□) HCl H₂O₂ strength Ex. 10 ◯1,000 85 0.1 ◯ 1,050 ◯ ◯ ◯ Ex. 11 ◯ 600 82 0.1 ◯ 660 ◯ ◯ ◯ Ex. 12 ◯ 80085 0.1 ◯ 830 ◯ ◯ ◯ Ex. 13 ⊚ 1,500 85 0.1 ◯ 1,500 ◯ ◯ ◯ Ex. 14 ⊚ 2,000 850.1 ◯ 2,020 ◯ ◯ ◯ Ex. 15 ⊚ 2,000 85 0.1 ◯ 2,020 ◯ ◯ ◯ Ex. 16 ⊚ 800 820.1 ◯ 820 ◯ ◯ ◯ Ex. 17 ⊚ 1,000 82 0.1 ◯ 1,020 ◯ ◯ ◯ Ex. 18 ⊚ 2,000 820.1 ◯ 2,010 ◯ ◯ ◯ Comp. X 3,000 87 0.2 X 3,650 X X — Ex. 8 Comp. Δ 5,00085 0.3 X 5,630 X Δ — Ex. 9 Comp. ⊚ 5,000 87 0.3 Δ 5,350 Δ X X Ex. 10Comp. ⊚ 8,000 85 0.3 Δ 8,500 Δ Δ X Ex. 11 Comp. X 1,000 87 2.0 X 1,370 XΔ — Ex. 12 Comp. X 3,000 87 3.0 X 3,100 X X — Ex. 13 Comp. X 20,000 885.0 X 20,400 X Δ — Ex. 14

[0238] The results given above show the following. The substrates whichhave a transparent conductive-coating film containing fine metalparticles of the invention have high durability and high scratchstrength. Furthermore, the coating liquids prepared in Examples 4 to 9(Examples 13 to 18) are characterized by having high stability and along pot life.

[0239] While the invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

[0240] This application is based on a Japanese patent application filedon Mar. 30, 2001 (Patent Application 2001-100356), the contents thereofbeing hereby incorporated by reference.

Industrial Applicability

[0241] According to the invention, since the fine metal particlescontain iron in a small amount within a specific range, not only theparticles retain high conductivity but also have properties similar toproperties of iron-containing alloys. The fine metal particles, whenused for forming a conductive coating film, can inhibit the nonironmetal from oxidizing or ionizing and inhibits particle growth. The filmcan hence be inhibited from suffering a decrease in conductivity orlight transmittance. Furthermore, the fine metal particles the surfaceof which has been oxidized show a high flow electrical current potentialand are excellent in dispersibility and stability.

[0242] The coating liquid for transparent conductive coating filmformation, which contains such fine metal particles, has a long potlife. When this coating liquid for transparent conductive coating filmformation is used, a substrate with transparent conductive coating filmhaving a transparent conductive coating film can be obtained which isexcellent in conductivity and electromagnetic shielding properties andhas high reliability. Furthermore, since the fine metal particles areexcellent in dispersibility and stability, the amount of an organicstabilizer to be used can be reduced and the removal of the organicstabilizer after coating film formation is easy. The organic stabilizercan hence be inhibited from remaining to impair conductivity. Inaddition, there is no need of burning the substrate at a temperature ashigh as 400° C. or above after coating film formation in order to removethe organic stabilizer as in related-art techniques, and the organicstabilizer can be removed at a low temperature. Consequently, not onlythe aggregation or fusion of fine metal particles which occurs inhigh-temperature burning can be prevented, but also the coating filmobtained can be prevented from having an impaired haze.

[0243] According to the process of the invention for producing finemetal particles, the fine metal particles described above can beefficiently obtained.

[0244] According to the invention, a coating liquid for transparentconductive coating film formation can be obtained which has a long potlife and can form a transparent conductive coating film excellent inconductivity and electromagnetic shielding properties and having highreliability.

[0245] Furthermore, according to the invention, a substrate withtransparent conductive coating film can be obtained which has atransparent conductive coating film excellent in conductivity andelectromagnetic shielding properties and having high reliability.

[0246] When this substrate with transparent conductive coating film isused as the front panel of a display device, the display device obtainedcan have excellent anti-reflection properties as well as excellentelectromagnetic shielding properties.

1. Fine metal particles comprising iron and noniron metal, characterizedby having an average particle diameter in the range of from 1 to 200 nmand an iron content in the range of from 0.1 to 3.0% by weight.
 2. Thefine metal particles as claimed in claim 1, characterized in that thenoniron metal is one or more metals selected from the group consistingof Au, Ag, Pd, Pt, Rh, Ru, Cu, Ni, Co, Sn, Ti, In, Al, Ta, and Sb. 3.The fine metal particles as claimed in claim 1 or 2, characterized inthat part of the surface of the fine metal particles is in the form ofan oxide and/or a hydroxide.
 4. The fine metal particles as claimed inany one of claims 1 to 3, characterized in that an aqueous dispersion inwhich the concentration of the fine metal particles is 0.5% by weighthas a flow electrical current potential in the range of from 50 to 300μeq/g.
 5. A process for producing fine metal particles, characterized byreducing a salt of iron and a salt of one or more noniron metals in asolvent comprising water and/or an organic solvent in the presence of areducing agent in such a manner as to result in fine metal particleshaving an iron content in the range of from 0.1 to 3.0% by weight. 6.The process for producing fine metal particles as claimed in claim 5,characterized in that after fine metal particles are produced byreducing the iron salt and the salt of one or more noniron metals, anoxidizing agent is further added to oxidize at least part of the surfaceof the fine metal particles.
 7. A coating liquid for forming atransparent conductive coating film, the coating liquid comprising thefine metal particles as claimed in any one of claims 1 to 4 and a polarsolvent.
 8. A substrate with transparent conductive coating film whichcomprises a substrate, a transparent conductive fine-particle layerdisposed on the substrate, and a transparent coating film formed on thetransparent conductive fine-particle layer and having a lower refractiveindex than the transparent conductive fine-particle layer, characterizedin that the transparent conductive fine-particle layer comprises thefine metal particles as claimed in any one of claims 1 to
 4. 9. Adisplay device characterized by having a front panel comprising thesubstrate with transparent conductive coating film as claimed in claim8, the transparent conductive coating film being formed on the outersurface of the front panel.